This invention relates to a method for transforming a video image into an image for a display matrix. The method applies particularly to the transformation of an image supplied by a monochrome CCD (charge coupled device) camera into an image for a LCD (liquid crystal display) type display matrix The invention also relates to a device for carrying out the method. The invention is particularly useful in devices for centering glass objects such as spectacle lenses.
In the remainder of this specification and claims, the expression "image" should be taken to mean both a real image, i.e. the real physically visible representation, as well as signals corresponding thereto and enabling said image to be represented on a cathode ray type tube (CRT tube) or display matrix.
One known type of CCD camera enables a standardized CCIR format image to be readily obtained: it is simple to use and has a compact structure. However, the image supplied can only be used on a cathode ray tube-type display device. This is a disadvantage as this type of screen, even though it ensures good image quality, takes up more space than a flat panel display, and maintaining the same image leads to a phenomenon of remanence. When used for measurement purposes, it also has disadvantages linked to the stability of the image over time and to problems of parallax due to the thickness of the glass of the screen and to its curved shape.
An LCD type display provides a simple solution to these problems: it takes up less space, is not subject to remanence if an image is maintained for a long time on the screen, it does not present problems with parallax or with the image drifting with the passage of time.
Despite this, no system exists allowing the image supplied by a CCD camera to be displayed on an LCD display.
This problem arises particularly in the field of optics. Opticians need to accurately situate spectacle glasses and lenses with respect to holders designed to receive them. Machines exist which enable the image of a lens to be viewed on a cathode ray screen at the same time as the image of its holder and, for example, of its frame. Such machines operate with a CCD type camera which films the image that the lens projects onto an opaque screen under the illumination supplied by the light from a light emitting diode. The image filmed by the CCD camera is projected onto a cathode ray screen, the image of the corresponding frame being projected at the same time.
This system could be further improved by using a flat LCD type display in place of the cathode ray tube.